Polypole broadband antenna array

ABSTRACT

A broadband antenna array comprising a plurality of like monopoles disposed vertically in either a triangular or quandrangular configuration wherein a monopole is provided at each apex. A coaxial feed point is provided at the center of the intersection of the diagonals of the particular configuration. By closely spacing the monopoles with respect to each other, omnidirectional patterns are achieved; and driving the monopoles in phase reduces by a ratio of a third the real and imaginary components of the system.

United States Patent Olson et al. 'Dec. 3, 1974 [54] POLYPOLE BROADBAND ANTENNA 2,029,015 1/1936 Bohm 343/844 ARRAY 2,299,585 lO/1942 Luck 343/844 [751 3; g;- gj gg i 3:5 3355- Primar Exam-neat Lieberman y p Attorney, Agent, or FirmR. S. Sciascia; G. J. Rubens [73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC [57] ABSTRACT [22] Filed Dec 10 1973 A broadband antenna array comprising a plurality of like monopoles disposed vertically in either a triangu- [21] Appl. No.: 423,339 lar or quandrangular configuration wherein a m0no pole is provided at each apex. A coaxial feed point is [52] U S Cl 343/844 343/857 provided at the center of the intersection of the diag- [51] "T 6 21/00 onals of the particular configuration. By closely spac- [58] Fieid 44 2 858 ing the monopoles with respect to each other, omnidirectional patterns are achieved; and driving the mono- [56} References Cited poles in phase reduces by a ratio of a third the real and imaginary components of the system. UNITED STATES PATENTS I 1,939,042 12/1933 Conrad 343/844 4 Claims 4 Drawing Figures PATENTELHEE 3.852.766

SHEET 20! 2 FIG.4

BACKGROUND OF THE INVENTION Existing broadband antenna arrays comprise compli cated mechanical structures which require special fabrication. The polypole broadband array disclosed herein, on the other hand, is an extremely simple device which operationally is equivalent to much larger and more complicated broadband antennas. Small land vehicles such as jeeps, tanks, and trucks by means of the present antenna can be provided with a broadband frequency capability of, for example, 30 76 MHz. Such coverage was not previously available because of the relatively large size of existing HF broadband antennas viz-a-viz the size of thevehicles. Existing broadband antennas, due to their large size are bulky, complicated mechanical structures which require many components such as insulators, turnbuckles, masts, and long lengths of wire. They are also very time consuming and expensive to fabricate and are easily affected by adverse weather conditions. The disclosed antenna comprises a simple structure which is operationally equivalent to much larger and complicated structures and which due to its superior mechanical strength permits the array to be used even under the most severe weather conditions.

SUMMARY OF THE INVENTION The disclosed inventive concept comprises a broadband antenna array for use in particular with small ships and light vehicles and for use in the VHF frequency range. The array comprises a plurality of like monopoles which are vertically disposed in either a triangular or quadrangular configuration upon a ground plane and wherein a monopole is rigidly mounted at each apex in a symmetrical manner. Energy is fed to the monopoles by means of a coaxial feed point which is located at the center of the intersection of the diagonals of the particular configuration selected. The monopoles comprise fiberglass whips which, by means of judicious, selectively predetermined spacing relative to each other, provide omnidirectional patterns; furthermore by driving the monopoles in phase, the real and imaginary components of the system are reduced by a factor of one-third or one-fourth. Superior mechanical strength is provided by the array which although simple in construction will endure and operate effectively even under severe weather conditions.

STATEMENT OF THE OBJECTS OF THE INVENTION The primary object of the present invention is to provide a simple, effective, relatively inexpensive and durable broadband antenna array for use in particular with small ships and small land vehicles.

It is another object of the present invention to provide a simple broadband antenna array having superior mechanical strength and which can be used under the most severe weather conditions without structural damage or operational effectiveness degradation.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a polypole broadband antenna array comprising the preferred embodiment of the present invention;

FIG. 2 is a side view of the array of FIG. 1;

FIG. 3 is a graphical representation of the azimuth pattern for the antenna array of FIG. 1 for 0 elevation.

FIG. 4 is the graphical representation of impedance vs. frequency for a typical polypole broadband antenna array.

DESCRIPTION OF THE PREFERRED EMBODIMENT As stated previously, the object of the inventive concept to be disclosed herein comprises providing an operationally effective, yet simple and inexpensive, broadband antenna array for use, in particular, in the UHF frequency range with small ships and light land vehicles. The objective, as will be disclosed hereinafter, is achieved by means of a polypole broadband antenna array which is simple in structure but which possesses superior mechanical strength wherein the array can be used as described above and under the most severe weather conditions without structural damage or operational effectiveness degradation damage resulting therefrom.

In FIG. 1, an array in a triangular configuration is disclosed. The array 10 comprises three monopole whip antennas 12, each of which is vertically disposed in one of the three apexes of an equilateral triangle configuration. Accordingly, with respect to the center feed point 14 each of the whip antennas is located from each of the other two whips.

For an array, as in FIG. 1, which is operational in the range of, for example, 6 30 MHz, each of the antennas 12 has a length of approximately 0.0224 u and is located at a distance of approximately 0.036 p. from the center point 14. The center point 14 comprises the energy feed point. Equal-length conductors 16 extend from the feed point to each antenna to provide energy thereto.

With respect to FIG. 2 which is a side view of FIG. 1, it can be seen that the three whip antennas 12 are vertically disposed, equal-length structures which may be of the fiberglass whip variety currently available. Each of the whip antennas 12 is supported and rigidly mounted upon a base insulator l8which for the frequencies of interest is about 1 foot long. Each antenna structure is then, in turn, rigidly mounted and attached to the ground plane 20.

The energy feed point 14 feeds energy as described above to each of the whip antennas by means of the conductors 16 which, as seen in FIG. 2, are connected to the whip antennas at an angle 0 of approximately 6 with respect to the center of the feed point. The inner conductor of the feeder coaxial cable is connected to each antenna 12 via the open feed wires and the outer conductor is connected to the ground plane 20.

The inventive concept could readily be utilized in a quadrangular configuration wherein a like whip antenna would be vertically disposed and mounted at each of the four corners of the configuration. The coaxial feed point would be located at the center of the intersection of the two diagonals of the configuration.

The operational advantages of the array shown in FIGS. 1 and 2 are achieved by means of the close spacing of the monopoles whereby omnidirectional paths are possible. Furthermore by driving the elements in phase, the real and imaginary components of the system are reduced by factors of one-third or one-fourth.

The array as disclosed in FIGS. 1 and 2 further provides superior mechanical strength which enables the broadband antenna array to be used advantageously with light land vehicles orsmall naval craft and which will endure severe weather conditions. The feed point 14 comprises a 50-ohm coaxial feed point located at the intersected diagonals of the triangle of FIGS. 1 and 2. The feed wires are attached to the center conductor of the coaxial feeder cable and are run to each monopole. As stated above the length of each monopole is approximately a quarter wavelength and the length of each feed wire is approximately 0.36 M at the lowest desired frequency.

The particular configuration seen in FIGS. 1 and 2 provides excellent omnidirectional patterns up to 30 elevation angle and a VSWR of less than 3:1 over a 5:1 bandwidth. Reference should be made to FIGS. 4 and 3 which graphically depict antenna impedance versus frequency, and azimuth patterns, respectively.

As stated above omnidirectional patterns are possible because of the close spacing of the whip antennas, and the maximum phase difference between each monopole is approximately 90 at the upper frequency of the array. The excellent impedance characteristics achieved by the array, as shown in FIG. 4, result from the fact that a single monopole has relatively high real and imaginary components when it is operated above or below quarter wavelength. Close spacing of three or four whips together in combination with driving them in phase effectively reduces the real and imaginary components by a factor of a third or a fourth. This combination places the focus of impedance points around the center of the Smith chart as shown in FlG. 4.

The distribution box shown in FIG. 2 is intended solely for weather protection requirements for the coaxial feeder cable and could be omitted if environmental requirements are not severe.

Thus it can be appreciated that an antenna array for use in broadband frequencies has been disclosed. The

array comprises a relativelysimple, inexpensive device which is easily adaptable to light land vehicles and small sea craft whereby such vehicles and craft are provided VHF antenna coverage. Furthermore, the array disclosed due to its superior mechanical strength can be used under the most severe weather conditions without damage, either operational or structural.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore'to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A broadband antenna array comprising:

a ground plane;

a plurality of identical, equal-length monopoles vertically disposed with respect to each other in a symmetrical manner at each of the apexes of a selectively predetermined geometrical configuration and upon said ground plane;

insulation means rigidly connected between each of said monopoles and said ground plane to provide a structurally rigid monopole configuration with respect to said ground plane; and,

energy feed means disposed and located in a central position with respect to all of said monopoles;

said array further including equal-length feed-wires connected from said feed means to each of said monopoles;

said feedwires being oblique to said ground plane.

2. The array of claim 1 wherein said configuration comprises an equilateral triangle and wherein said feed means is located at the intersection of the perpendicular bisectors of the sides of said triangle.

3. The array of claim 2 wherein said monopoles comprise whip antennas having a length substantially equal to which are located at a distance from said feed means substantially equal to .0364L.

4. The array of claim 1 wherein the angle formed by each of said feedwires and said ground plane is approximately 6.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 52,766 Dated December 3, 197A I v ntor( Irving G. Olson et a1.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In column 2, line 17, "UHF" should read --VHF--.

In column 2, line 35, "0.022%" should read --0.22 +X--.

In column 2, line 36, "u" should read In column 3, line 15, "0.36 should read in claim 3, line 3, after "to" there should be inserted "ox/ In claim 3, line should read Signed and sealed this 18th day of March 1975.

(SEAL) Attest:

C. I-KARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks FORM PO-1050 (10-69) I T USCOMM-DC 60376-P69 u.s.sovznuncmrmmmoomc: 569 93o 

2. The array of claim 1 wherein said configuration comprises an equilateral triangle and wherein said feed means is located at the intersection of the perpendicular bisectors of the sides of said triangle.
 3. The array of claim 2 wherein said monopoles comprise whip antennas having a length substantially equal to which are located at a distance from said feed means substantially equal to .036 Mu .
 4. The array of claim 1 wherein the angle formed by each of said feedwires and said ground plane is approximately 6*. 